Here is how I play duke3d
The game must support native joystick. I implemented support for keys, but this sucks. Try check first in-app help about tilt, I tried explain a lot of there.
But, simply, you need enabled native 2axis joystick and you must calibrate it. Then if you are able play game with virtual joystick set to 2axis, you can use tilt. I, for example, have virtual joystick on screen for calibration, then I hide it and enable tilt.